1. Technical Field
The disclosure relates in general to an amplifier circuit, and more particularly to a variable gain amplifier circuit.
2. Description of the Related Art
In application of wireless network (such as Wi-Fi), a gain may need to be switched. Normally, the gain may be increased or varied by increasing or switching a transmission power and a reception power. The conventional gain switch to an amplifier may implemented by adjusting transconductance of a RF amplifier or by signal bypass.
In adjusting the gain by adjusting the transconductance, the current flowing through the amplifier must be reduced in order to reduce the gain. However, the linearity of the amplifier will be reduced at the same time.
If the gain is adjusted by way of signal bypassing, the current flowing through the amplifier does not change and the linearity of the amplifier is thus maintained. However, if the gain is adjusted at a large range, it needs more signal bypass paths. Consequently, extra parasitic capacitance is generated, making the amplifier unable to be operated at a high frequency.